1. Field of the Invention
This invention relates to near net shape casting of metal articles by utilizing a focused high energy beam to melt successive layers of powder feedstock onto a substrate. Rapid build up of the article is achieved by forming a mold from the powder metal to laterally support a thick layer of the powder melted on each pass.
2. Background Information
The conventional practice of melting and casting of metals and alloys frequently encompasses considerable expenditures in time and materials for preparation of the necessary casting molds and/or dies. In many cases, cast products are then machined to final dimensions which incurs additional costs. Furthermore, some alloys are very difficult and therefore costly, to machine. In some instances, due to mold and/or die deterioration, the number of cast parts obtainable from a given set of fixturing may be limited, which also increases costs.
Recently, innovative advances have led to the development of processes for producing so-called near net shape parts, which offer advantages in minimization of post-casting operations. Some of these procedures still require casting, but involve molding powdered metal to more precise shapes. Other techniques include building up bulk metal products such as cylinders by applying successive layers of metal using conventional welding techniques.
U.S. Pat. No. 4,323,756 teaches a method of producing near net shape metallic articles by depositing multiple thin layers of wire or powder metal feedstock to a substrate using a high energy laser beam or electron beam. An essential feature of the process of this patent is that the volume of substrate melted on each pass exceeds the volume of melted powder metal added, such that each layer is melted at least twice, which is said to improve the metallurgical structure of the finished article. The maximum thickness of layers added by this process is said to be 0.005 inches so that hundreds or even thousands of layers are added to form the finished product.
A primary object of the present invention is to provide apparatus and a process for making near-net shape articles from powder metal which can be built up rapidly.
Another object of the invention is to provide such an apparatus and method which utilize the powder metal itself to form a mold which provides lateral support for the thick layers of powder metal required for rapid build up of the article.
Yet another object of the invention is to provide such an apparatus and method which provides for the removal of heat generated by the energy beam from the substrate on which the article is formed.
Still another object of the invention is to provide a method by which articles built up from layers of melred powder metal can be separated from the substrate on which they are formed.